1. Field of the Invention
This invention relates to a catalyst composition containing platinum, rhenium and iridium where (1) platinum and rhenium and (2) iridium and rhenium are contained on separate particles of a refractory support and to the reforming of selected petroleum fractions in the presence of this catalyst to obtain gasoline of high octane number.
2. Description of the Prior Art
Catalysts intended for use in reforming operations wherein hydrocarbon fractions such as naphthas or gasolines or mixtures thereof are treated to improve the anti-knock characteristics thereof are well known in the petroleum industry and have been the subject of intensive investigation in both the patent and technical literature.
It has heretofore been proposed to employ platinum metal-containing catalysts for promoting reforming. Such catalysts are necessarily characterized by a certain amount of acidity. One type of reforming catalyst which has been used commercially consists of alumina base material having platinum metal impregnated thereon, with the acidity characteristics being contributed by a small amount of halogen incorporated in the catalyst.
In more recent years, multi-metallic reforming catalysts have been the subject of patent and technical literature. These catalysts contain platinum together with one or more additional metals, such as ruthenium, germanium, iridium, palladium, rhenium, osmium, rhodium, copper, silver, tin or gold deposited on a refractory support which also contains a specified amount of halogen. Representative of these multi-metallic reforming catalysts are those containing platinum and rhenium on platinum and iridium such as described in U.S. Pat. Nos. 2,848,377; 3,415,737 and 3,953,368. The latter patent reports certain advantages when platinum and iridium are present on a refractory support as highly dispersed polymetallic clusters in which the metallic atoms are separated by a distance of about 2.5-4.0 Angstroms.
It has also heretofore been known to conduct catalytic reforming utilizing a catalyst consisting essentially of a particularly defined mixture of particles of a porous carrier impregnated with a small amount of platinum and particles of an acidic cracking component. Representative disclosures of such prior art are found in U.S. Pat. Nos. 2,854,400; 2,854,403; 2,854,404. Also, it has been suggested, for example, in German OS No. 26 27 822 to conduct reforming in the presence of a catalyst constituting a mixture of platinum on one solid catalyst and rhenium on a second solid carrier.
The use of trimetallic catalysts is also known in the reforming art and, in fact, single particle platinum, rhenium, and iridium catalysts on an alumina support are specifically taught in U.S. Pat. Nos. 3,578,583; 3,617,520; 3,487,009; as well as an article in International Chemical Engineering, 1978.
Recently, there have been advances made in the art on using separate particles containing platinum and rhenium on one support and iridium on another support. Patents of this general type are U.S. Pat. No. 4,288,348; as well as U.S. Pat. No. 4,264,475. All of the above catalysts, while possessing certain advantages, are nevertheless subject to improvement with regard to the provision of a reforming catalyst which provides a high yield of gasoline of high octane number over an extended period of time.